Apparatus for determining mold cavity pressure



April 36 1946 E. J. GlBBoNs Ell-Al. 2,399,342.,

PPARATUS FOR DETERMINING MOLD CAVITY PRESSURE Filed sept. 12, 1944 INVENTOR ATTORNEY i heating cylinder Patented Apr. 30, 1946 f NirEo "STATI-:sf AAT1?. f

' APPARATUS FOR DETRG MLD CAVITY PRESSURE sewers r. Gibbons ena Thomas M. oNen, sr.,

New York, N.. Y.,

assignors to erican A Cyanarnid'Company, 'New York, N. Y., a corporation of Maine Application September l2, 1944i, Serial No. 5535708 2 Claims. (Ci. i3-39S) The present invention relates to means for determining the pressure in a mold cavity.

In present day molding practice of thermoplastic material such as by injection molding itA f is commonly assumed that the pressure in the -mold cavity at the time of molding is some fraction of the unit pressure on the ram. This irac tion while unique in each case as it depends on many empirical factors, is always assumed.

Due to the fact that no method has been here toiore devised for independently determining the ture oi' the solidiiying: thermoplastic material when it hits the mold cavity this assumption lhas sometimes led to detrimental results.

It is the'principal object of the present invention to devise means whereby the mold cavity pressure can be measured both at the instant of injection ci the thermoplastic material and during the hardening cycle with reasonable accuracy.

- It is another obiectof the invention to provide a. combined mechanical and electrical hook-up' whereby the pressure in the mold cavity at 'the pressure in the mold cavity due to thevery na moment of injection and during the hardening cycle may be read directly and conveniently in pounds per square inch inasmuch as these units are used in determining the pressure on the head of the ram in the injection chamber. I

To this end the to feed a thermoplastic material` thereto under pressure, a. loading pin having one face within the mold cavity and subject v to the pressure therein, the pin extending outside formed between the complementary parts 8 and 9 constituting a mold. A A

'I'he part d of the mold is provided with a mov- ,able loading pin it the face iil of which is 'ush with one surface 'ofthe mold cavity. The other end olf'the. pin engages a beam i2 the part t of the mold.

Secured to the tension face of the beam i2 is v an active strain gauge I3 and a dummy gauge it, the latter being fastened to the beam i2 but out of substantial contact therewith though in close proximity to the active gauge it.

4the circuit and causes the galvanometer to de- 'lect, all of which is of the usual construction.

invention contemplatesa mold cavity, with means the cavity and -against a beam, subject to distortion by reason oi the pressure within the mold through the pin, and a strain gauge secured to the tension face of the beam and electrically connected to an instrument whereby the change in electrical resistance of the gauge when the beam is under load' may be read. v

The invention further .contemplates the novell combination, construction, andarrangement of mrts and the method more fully hereinafter shown and described in the accompanying draw'- ing in which the single iigure is a'diag'rammatic representation of one embodiment of the' invention.

Referring now to the form illustrated, the usual injection cyiinderis shown at i having a piston or ram 2, one end oi' which operates within a thermoplastic material t from the cylinder" throughnozzle 5 and une' s te e mold cavity' v e5 By means oi the variable rheostat i9 the voltage applied to the bridge may be so adjusted that the galvanometer is caused to read directly in terms of the pressure in the mold cavity, that is in pounds per square inch.

This last may be readily accomplished by placing the strain gauge in a testing machine of the Olsen type so as to simulate mold loading.- By testing this strain gauge in uniform increments of load, the galvanometer reading may be so calibrated as to read in pounds per square inch.

The dummy gauge It, being similar in all aspects to the active gauge i3 and secured to the beam i2 though not subject to strain when thebeam is loaded, serves to compensate through the electrical instrument Il for any temperature Achanges which may occur in the beam itself and which would otherwise cause an error in the reading of the circuit unbalances when the active A gauge n3 is operating. l.

It will thus be seen that upon the application otpressure to the injection cylinder, it is transmitted through piston or ram 2 which forces the v cavity Y thermoplastic material d into thev mold 'i where solidiiication taires piace. The head il of loading pin iu being subjected to the pressure actually occurring within the mold cavity itself, is transmitted'throush the'inearn i2 and may secured to measured by a .D

be read direct through deflection o! the salvannmeter needle 20.

As indicating the danger of assuming the pressure in the mold cavity it was found for instance, that when P1 was 1500 pounds per square inch,

" P, was 35,000 pounds per square men while P:

therein, means to feed a thermoplastic material I 'thereto under pressure, a beam mounted on the exterior of the mold, a movable loading pin extending through a wall of the mold with an end surface flush with one surface oi the mold cavity and one end engaging the beam, a strain gauge havinga iilament, the electrical resistance no under a strain.

0f which. varies with m man. secured to the tension sideof the beam. and a measuring instruu mentfeiectrically connectedto said mament whereby the change in electrical resistance o! the filament may he read when the filament.y is

under a strain.

2. In combination a moldhaving a cavityY therein, means to feed a thermoplastic material thereto under pressure. `a beam mounted exteriorly of the mold, a movable loading pin with an end surface ush with one surface of the mold cavity, the pin extending tlm'mghA a wall of the mold cavity and engaging the beam, a strainl gauge having a lamentfthe electrical resistance o f which varies with its strain, secured to the' tension side o! the beam, and a measuring instrument electrically connected to said .iiiament whereby the change in electrical resistance of the iilament may be read when the mament is EDWARD J. GranoNs.. 'moms M. o'NEm, Ja. 

